Programming nonvolatile memory device using program voltage with variable offset

ABSTRACT

A method of programming a nonvolatile memory device comprises applying at least one test program pulse to selected memory cells located in a scan read area, performing a scan read operation on the selected memory cells following application of the at least one test program pulse to detect at least one one-shot upper cell, calculating an offset voltage corresponding to a scan read region at which the scan read operation is performed, setting a program start bias using the offset voltage, and executing at least one program loop using the program start bias.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.13/969,651, filed Aug. 19, 2013, which claims priority under 35 U.S.C.§119 to Korean Patent Application No. 10-2012-0112954 filed Oct. 11,2012, the subject matter of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The inventive concept relates generally to memory technologies. Moreparticularly, certain embodiments of the inventive concept relate tononvolatile memory devices and related methods of programming.

Nonvolatile memory devices can be found in a wide variety of electronicdevices, including, for instance, tablet computers, mobile phones,digital cameras, and many others. As a consequence of the increasingperformance demands of these and other devices, there is a generaldemand for nonvolatile devices having increased storage capacity.Accordingly, to address this demand, researchers continue to developtechniques for improving existing nonvolatile memory technologies, inaddition to developing new nonvolatile memory technologies.

Two common approaches for increasing the storage capacity of nonvolatilememory devices are to decrease the size of memory cells and to increasethe number of bits per memory cell. These approaches, however, tend todecease the operating margins of the devices, creating increasedpossibility of errors. Accordingly, as a complement to the aboveapproaches, researchers also continue to develop approaches formaintaining the reliability of the memory devices.

SUMMARY OF THE INVENTION

In one embodiment of the inventive concept, a method of programming anonvolatile memory device comprises applying at least one test programpulse to selected memory cells located in a scan read area, performing ascan read operation on the selected memory cells following applicationof the at least one test program pulse to detect at least one one-shotupper cell, calculating an offset voltage corresponding to a scan readregion at which the scan read operation is performed, setting a programstart bias using the offset voltage, and executing at least one programloop using the program start bias.

In another embodiment of the inventive concept, a method of programminga nonvolatile memory device comprises determining whether to use anoffset index stored at an offset index register according to a blockaddress of a memory block comprising memory cells to be programmed,applying a test program pulse to the memory cells, applying a testverification pulse to the memory cells to verify programming by the testprogram pulse, performing a scan read operation of the memory cells,changing the offset index in the offset index register according to aresult of the scan read operation, setting a program start bias usingthe offset index, and iterating program loops using the program startbias until a program operation is passed. The scan read operationcomprises iterating operations comprising determining whether a numberof off cells exceeds a predetermined value, increasing the offset indexwhere the number of off cells does not exceed the predetermined value,and performing a read operation using a scan read voltage correspondingto the offset index, and entering the setting a program start bias wherethe number of off cells exceeds the predetermined value.

In yet another embodiment of the inventive concept, a nonvolatile memorydevice comprises a controller configured to apply at least one testprogram pulse to selected memory cells located in a scan read area,perform a scan read operation on the selected memory cells followingapplication of the at least one test program pulse to detect at leastone one-shot upper cell, calculate an offset voltage corresponding to ascan read region at which the scan read operation is performed, set aprogram start bias using the offset voltage, and execute at least oneprogram loop using the program start bias.

These and other embodiments of the inventive concept can potentiallyimprove performance and power consumption of nonvolatile memory devicesby calculating an offset using a scan read operation and performing aprogram operation using the offset calculated.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate selected embodiments of the inventive concept.In the drawings, like reference numbers indicate like features.

FIG. 1 is a block diagram of a nonvolatile memory device according to anembodiment of the inventive concept.

FIG. 2 is a perspective view of a memory block in FIG. 1 according to anembodiment of the inventive concept.

FIG. 3 is a diagram illustrating an equivalent circuit of the memoryblock in FIG. 1 according to an embodiment of the inventive concept.

FIG. 4 is a diagram illustrating a one-shot program operation accordingto an embodiment of the inventive concept.

FIG. 5 is a flowchart illustrating a method of programming a nonvolatilememory device according to an embodiment of the inventive concept.

FIG. 6 is a threshold voltage diagram illustrating a method ofprogramming a nonvolatile memory device according to an embodiment ofthe inventive concept.

FIG. 7 is a timing diagram for the method of FIG. 5.

FIG. 8 is a flowchart illustrating a method of programming a nonvolatilememory device according to an embodiment of the inventive concept.

FIG. 9 is a flowchart illustrating a scan read method according to anembodiment of the inventive concept.

FIG. 10 is a diagram illustrating a method of programming a nonvolatilememory device according to an embodiment of the inventive concept.

FIG. 11 is a timing diagram for the method of FIG. 10.

FIG. 12 is a flowchart illustrating the method of FIG. 10.

FIGS. 13A to 13E show various combinations of an offset period andprogram loops.

FIG. 14 is a block diagram illustrating an on-chip buffered programmingmethod according to an embodiment of the inventive concept.

FIG. 15 is a block diagram illustrating a memory system according to anembodiment of the inventive concept.

DETAILED DESCRIPTION

Embodiments will be described in detail with reference to theaccompanying drawings. The inventive concept, however, may be embodiedin various different forms, and should not be construed as being limitedonly to the illustrated embodiments. Rather, these embodiments areprovided as examples so that this disclosure will be thorough andcomplete, and will fully convey the concept of the inventive concept tothose skilled in the art. Accordingly, known processes, elements, andtechniques are not described with respect to some of the embodiments ofthe inventive concept. Unless otherwise noted, like reference numeralsdenote like elements throughout the attached drawings and writtendescription, and thus descriptions will not be repeated. In thedrawings, the sizes and relative sizes of layers and regions may beexaggerated for clarity.

It will be understood that, although the terms “first”, “second”,“third”, etc., may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another region, layer or section. Thus, a firstelement, component, region, layer or section discussed below could betermed a second element, component, region, layer or section withoutdeparting from the teachings of the inventive concept.

Spatially relative terms, such as “beneath”, “below”, “lower”, “under”,“above”, “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or operation in addition tothe orientation depicted in the figures. For example, if the device inthe figures is turned over, elements described as “below” or “beneath”or “under” other elements or features would then be oriented “above” theother elements or features. Thus, the terms “below” and “under” canencompass both an orientation of above and below. The device may beotherwise oriented (rotated 90 degrees or at other orientations) and thespatially relative descriptors used herein interpreted accordingly. Inaddition, it will also be understood that when a layer is referred to asbeing “between” two layers, it can be the only layer between the twolayers, or one or more intervening layers may also be present.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the inventiveconcept. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items. Also, the term “exemplary” is intended to referto an example or illustration.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to”, “coupled to”, or “adjacent to” anotherelement or layer, it can be directly on, connected, coupled, or adjacentto the other element or layer, or intervening elements or layers may bepresent. In contrast, when an element is referred to as being “directlyon,” “directly connected to”, “directly coupled to”, or “immediatelyadjacent to” another element or layer, there are no intervening elementsor layers present.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this inventive concept belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and/orthe present specification and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

FIG. 1 is a block diagram of a nonvolatile memory device according to anembodiment of the inventive concept.

Referring to FIG. 1, a nonvolatile memory device 100 comprises a memorycell array 110, an address decoder 120, an input/output circuit 130, andcontrol logic 140.

Memory cell array 110 is connected to address decoder 120 through wordlines, at least one string selection line SSL, and at least one groundselection line GSL and to input/output circuit 130 through bit lines.Memory cell array 110 comprises multiple memory blocks BLK1 to BLKz eachcomprising multiple three-dimensional memory cells arranged along afirst direction, a second direction different from the first direction,and a third direction perpendicular to a plane formed in the first andsecond directions.

Address decoder 120 is connected to memory cell array 110 via word linesWL, at least one string selection line SSL, and at least one groundselection line GSL. Address decoder 120 selects word lines WL, the atleast one string selection line SSL, and the at least one groundselection line GSL using a decoded row address. Address decoder 120decodes a column address of an input address ADDR, and a resultingdecoded column address DCA is transferred to input/output circuit 130.In some embodiments, address decoder 120 comprises a row decoder, acolumn decoder, an address buffer, and so on.

Input/output circuit 130 is connected to memory cell array 110 via thebit lines. Input/output circuit 130 selects the bit lines using thedecoded column address DCA from address decoder 120.

Input/output circuit 130 receives data from an external device (e.g., amemory controller) and stores it in memory cell array 110. Input/outputcircuit 130 reads data from memory cell array 110 and outputs it to theexternal device. Input/output circuit 130 further reads data from afirst region of memory cell array 110 and stores it in a second regionthereof. In some embodiments, input/output circuit 130 is configured toperform a copy-back operation.

Control logic 140 is configured to control an overall operation of thenonvolatile memory device 100. Control logic 140 operates responsive tocontrol signals CTRL or a command transferred from the external device.Control logic 140 performs a scan read operation to calculate an offsetvoltage for a one-shot program operation.

The term “one-shot program operation” refers to a multi-bit programoperation in multiple data values are programmed to a selected memorycell (or cells) by changing its threshold voltage from an initial stateto a target state. For instance, in a one-shot program operation mayprogram two bits to a two-bit memory cell by changing its thresholdvoltage from an erase state to a programmed state. As will be apparentfrom the following description, the change of threshold voltage may beperformed, for instance, using an incremental step pulse programming(ISPP) technique.

The offset voltage for the one-shot program operation is a valueindicating an adjustment to a program voltage used in the one-shotprogram operation. For instance, the value can be applied as a bias toan initial program voltage used in the ISPP technique. The valuetypically reflects contextual information about memory cells to beone-shot programmed, such as a structural location, a level ofdeterioration, a temperature.

The scan read operation comprises a read operation performed on apredetermined read area (hereinafter, referred to as a “scan read area”)in a predetermined interval. Control logic 140 typically performs thescan read operation to detect off cells among selected memory cellsafter applying of a test pulse (a test program pulse and a testverification pulse) to the selected memory cells, and it calculates theoffset voltage for the scan read area for which the scan read operationis performed.

Control logic 140 comprises an offset index register (OIR) 142 thatstores an offset index corresponding to an offset voltage. Control logic140 changes a program start bias of at least one program loop using theoffset index stored at the offset index register 142.

FIG. 2 is a perspective view of a memory block in FIG. 1 according to anembodiment of the inventive concept.

Referring to FIG. 2, four sub-blocks are formed on a substrate. Each ofthe sub-blocks is formed by stacking at least one ground selection lineGSL, multiple word lines WL, and at least one string selection line SSLon the substrate and separating a resultant structure by word line cutsWL Cut. Herein, at least one string selection line SSL is separated bystring selection line cuts SSL Cut. Although not illustrated in FIG. 2,each of the word line cuts WL Cut may comprise a common source line CSL.Common source lines included in the word line cuts WL Cut are connectedin common.

In the example of FIG. 2, a structure between word line cuts is assumedto be a sub-block. However, the inventive concept is not limitedthereto. For example, a structure between a word line cut and a stringselection line cut can be defined as a sub-block.

A block according to an embodiment of the inventive concept may have amerged word line structure in which two word lines are merged into one.

FIG. 3 is a diagram illustrating an equivalent circuit of a memory blockaccording to an embodiment of the inventive concept.

Referring to FIG. 3, a memory blocks BLKi comprises cell strings CS11,CS12, CS21, and CS22 each comprising a string selection transistor SST,a ground selection transistor GST, and memory cells MC1 to MC6. In eachof cell strings CS11, CS12, CS21, and CS22, memory cells MC1 to MC6 areconnected between string selection transistor SST and ground selectiontransistor GST.

Control gates of ground selection transistors GST in cell strings CS11,CS12, CS21, and CS22 are connected in common to a ground selection lineGSL. One end of each ground selection transistor GST is connected tomemory cells MC1, and another other end is connected in common to acommon source line CSL.

In cell strings CS11, CS12, CS21, and CS22, memory cells MC1 areconnected in common to a word line WL1, memory cells MC2 are connectedin common to a word line WL2, memory cells MC3 are connected in commonto a word line WL3, memory cells MC4 are connected in common to a wordline WL4, memory cells MC5 are connected in common to a word line WL5,and memory cells MC6 are connected in common to a word line WL6.

In cell strings CS11 and CS12, control gates of string selectiontransistors SST are connected to a string selection line SSL1. In cellstrings CS21 and CS22, control gates of the string selection transistorsSST are connected to a string selection line SSL2. In cell strings CS11and CS21, one end of each string selection transistor SST is connectedto a bit line BL1, and another end is connected to memory cells MC6. Incell strings CS12 and CS22, one end of each string selection transistorSST is connected to a bit line BL2, and another end is connected tomemory cells MC6.

For ease of description, rows, columns, and heights may be defined. Adirection in which string selection lines SSL1 and SSL2 extend may be arow direction (or, a first direction). Cell strings CS11 and CS12 arearranged along the row direction to form a first row. Cell strings CS21and CS22 are arranged along the row direction to form a second row.

A direction in which bit lines BL1 and BL2 extend may be a columndirection (or, a second direction). Cell strings CS11 and CS21 may bearranged along the column direction to form a first column. Cell stringsCS12 and CS22 may be arranged along the column direction to form asecond column. A direction proceeding from ground selection transistorsGST to string selection transistors SST may be a height.

Memory cells MC1 and MC6 form a three-dimensional structure in whichmemory cells MC1 to MC6 are arranged along the row and column directionsand stacked along a height direction (or, a third direction). Memorycells at the same height are connected in common to a word line, andmemory cells at different heights are connected to respective wordlines. String selection transistors SST in the same row are connected incommon to a string selection line SSL1/SSL2, and string selectiontransistors SST in different rows are connected to respective stringselection lines SSL1 and SSL2. String selection transistors SST in thesame column are connected to the same bit line BL1/BL2, and stringselection transistors SST in different columns are connected torespective bit lines BL1 and BL2.

Each of memory cells MC1 to MC6 may store two or more bits. In otherwords, each of memory cells MC1 to MC6 may be a multi-level cell.

Although FIG. 3 shows a memory block BLKi comprising four cell stringsCS11, CS12, CS21, and CS22, the inventive concept is not limited to thisnumber of cell strings. In general, at least two or more cell stringsmay be provided along a row direction or a column direction. Similarly,although FIG. 3 shows each cell string comprising six memory cells MC1to MC6, the inventive concept is not limited to this number of memorycells in each cell string. In general, each cell string may comprise twoor more memory cells along the height direction. Although FIG. 3 showsground selection transistors GST connected in common to a groundselection line GSL, memory block BLKi may be changed or modified suchthat ground selection transistor GST in the same row are connected incommon to a ground selection line and ground selection transistor GST inanother row are connected in common to another ground selection line.Although FIG. 3 shows each cell string comprising a string selectiontransistor SST and a ground selection transistor GST, in general, eachcell string can be configured to include two or more string selectiontransistors SST and two or more ground selection transistors GST. Invarious embodiments, at least one of memory cells MC1 to MC6 in eachcell string may be used as a dummy memory cell.

A nonvolatile memory device according to certain embodiments of theinventive concept may perform a multi-bit program operation using aone-shot program operation using an offset (e.g., an offset voltage, anoffset time, etc.).

FIG. 4 is a diagram illustrating a one-shot program operation accordingto an embodiment of the inventive concept. The one-shot programoperation of FIG. 4 is used to program a 2-bit MLC.

Referring to FIG. 4, the one-shot program operation changes an originalerase state E0 to one of an erase state E, a first program state P1, asecond program state P2, and a third program state P3. FIG. 4illustrates a first verification voltage VF1 for verifying first programstate P1, a second verification voltage VF2 for verifying second programstate P2, and a third verification voltage VF3 for verifying thirdprogram state P3.

For ease of description, it is assumed that a nonvolatile memory device100 is a vertical NAND flash memory device (or, called “VNAND”). Anoffset may exist between memory blocks or between word lines accordingto a process variation in A VNAND structure. A conventional nonvolatilememory device may change a program start bias of an MSB programoperation according to the number of program pulses applied at an LSBprogram operation to revise such offset. However, it may be difficult toapply the one-shot program operation to the conventional nonvolatilememory device. The reason may be that the one-shot program operationdoes not include the LSB program operation. Further, it is difficult touse the number of program pulses applied as an offset between wordlines. On the other hand, the inventive concept may include detecting anoffset according to a structural cell characteristic using a scan readoperation and performing a one-shot program operation using the detectedoffset.

FIG. 5 is a flowchart illustrating a method of programming a nonvolatilememory device according to an embodiment of the inventive concept.

Referring to FIGS. 1 to 5, in operation S110, a test program pulse isapplied to memory cells. Herein, the test program pulse may have apredetermined level. Afterwards, in operation S120, the methoddetermines whether to detect one-shot upper cells. As used herein, theterm “one-shot upper cell” refers to a memory cell whose thresholdvoltage changes by a predetermined amount in response to the testprogram pulse. In certain embodiments, the detection of one-shot uppercells is accomplished according to a result of a verification operationperformed using a predetermined verification voltage. For example, aselected memory cell may be detected as a one-shot upper cell where aresult of the verification operation indicates that the selected memorycell is an off cell.

In operation S130, a scan read operation on a predetermined area isperformed to detect one-shot upper cells. Herein, the predetermined areamay be changed according to contextual information such as a temperatureof a nonvolatile memory device 100, wear-leveling (e.g., P/E cycle) of amemory block including memory cells, an address of a memory blockincluding memory cells, and so on.

In operation S140, a program start bias is determined according to aresult of the scan read operation. For example, if the number ofone-shot upper cells exceeds a predetermined value, a default level ofthe program start bias may increase by a predetermined offset value.

In operation S150, program loops are iterated using the determinedprogram start bias until a program operation is passed. Returning tooperation S120, if a one-shot upper cell detection operation is notrequired, in operation S155, program loops may be iterated using adefault program start bias.

The method in FIG. 5 comprises detecting one-shot upper cells (S120),but the inventive concept is not limited thereto. For example, themethod of FIG. 5 can be modified to include directly performing the scanread operation to calculate an offset voltage without detecting ofone-shot upper cells and determining the program start bias according toa calculated offset voltage.

FIG. 6 is a diagram illustrating a method of programming a nonvolatilememory device according to an embodiment of the inventive concept.

Referring to FIG. 6, an offset voltage is determined by applying a loopstart voltage Vini to selected memory cells, performing a verificationread operation using a verification voltage VF1 of a first program stateP1, determining whether to perform a scan read operation according to aresult of the verification read operation, and performing a scan readoperation on a scan read region SRR on the basis of the verificationvoltage VF1.

In some embodiments, the scan read operation is performed underconditions where a top point VTP decreases by a predetermined voltage.The predetermined voltage may be, for instance, a unit voltage in theISPP technique. Where the scan read operation progresses downward, thetop point VTP of the scan read region SRR may correspond to the firstverification voltage VF1, and a down point VDN thereof may correspond toa voltage at which one-shot upper cells are first detected (i.e., offcells are first detected).

In some other embodiments, the scan read operation may be performedunder conditions where down point VDN increases by a predeterminedvoltage. When the scan read operation progresses upward, top point VTPof the scan read region SRR may correspond to a voltage when the numberof one-shot upper cells does not exceed a predetermined number, and thedown point VDN may be a predetermined voltage (e.g., a read voltage onP1). Scan read region SRR is not necessarily limited to the abovedescription, and can take alternative forms.

As indicated by the foregoing, the one-shot program operation may changea program start bias of at least a next program loop according to anoffset voltage Voffset corresponding to the scan read region SRR. Forexample, if the scan read region SRR is detected to be relatively wide,a program start bias may be higher than that when the scan read regionSRR is relatively narrow. On the other hand, if the scan read region SRRis detected to be relatively narrow, a program start bias may lower thanthat when the scan read region SRR is relatively wide. In case of aprogram operation where the scan read region SRR is unnecessary, adefault program start bias may be used.

FIG. 7 is a timing diagram for the method of FIG. 6.

Referring to FIG. 7, the method comprises an offset setting period andprogram loops. In the offset setting period, after a test program pulseof a loop start voltage Vini is applied, a verification operation isperformed using a test verification pulse of a first verificationvoltage VF1. Whether to perform program loops Loop1 to Loop N in adefault path or in an offset path is determined according to a result ofthe verification read operation. For example, if a result of theverification read operation indicates that the number of off cellsexceeds a predetermined number, a one-shot program operation may beperformed via the default path. On the other hand, if a result of theverification read operation indicates that the number of off cells isless than the predetermined number, the one-shot program operation maybe performed via the offset path.

Although FIG. 7 illustrates an example in which a test program pulse isapplied, the inventive concept is not limited thereto. For example, atleast two test pulses may be applied in the offset setting period. Inthis case, the at least two test pulses may have the same level ordifferent levels. Although FIG. 7 illustrates an example in which a testverification pulse of the first verification voltage VF1 is applied, theinventive concept is not limited thereto. For example, in the offsetsetting period, a verification read operation may be performed using atest verification pulse after at least one test program pulse isapplied.

As illustrated in FIG. 7, the offset setting period may include a scanread operation for detecting one-shot upper cells. An offset voltageVoffset applied to a program start bias may be determined according to aresult of the scan read operation.

A program loop period may proceed differently according to the defaultand offset paths. First, referring to the default path, at a firstprogram loop Loop 1, a first program pulse (Vini+ΔVpgm) higher by a loopincrement ΔVpgm than loop start voltage Vini is applied and verificationoperations may be performed using multiple verification pulses. Herein,the loop increment ΔVpgm may have a constant value or a value variedaccording to the number of loops. Herein, the verification pulses may bevoltages corresponding to multiple program states (e.g., P1, P2, and P3in FIG. 4).

In the default path, at a second program loop Loop 2, a second programpulse (Vini+2ΔVpgm) higher by the loop increment ΔVpgm than the firstprogram pulse is applied and verification operations may be performedusing the verification pulses. The remaining program loops in thedefault path may be performed in the same manner as described above.

In the offset path, a program start bias (Vini+Voffset) determinedaccording to a scan read operation is applied to a first program loop.The remaining program loops in the offset path may be performedsubstantially the same as the default path. Herein, the program startbias may include loop start voltage Vini and offset voltage Voffset.Herein, offset voltage Voffset may be a voltage corresponding to a scanread region SRR (See, FIG. 6).

In particular, in the offset path, at a first program loop Loop 1, afirst program pulse of a program start bias (Vini+Voffset) is appliedand verification operations are performed using the verification pulses.In a second program loop Loop 2, a second program pulse (Vini+2ΔVpgm)higher by the loop increment ΔVpgm than the first program pulse(Vini+ΔVpgm) is applied and verification operations are performed usingthe verification pulses. The remaining program loops are performed thesame as the default path.

FIG. 8 is a flowchart illustrating the method of FIG. 6 according to anembodiment of the inventive concept. For convenience, the method of FIG.8 will be described with reference to the device of FIG. 1, although themethod is not limited to this device.

A program command, an address, and write data are provided to anonvolatile memory device 100. In operation S211, control logic 140 ofnonvolatile memory device 100 determines whether a block address of theinput address is different from a block address of a previous programoperation. If a block address of the input address is different from ablock address of a previous program operation, in operation S212, anoffset index m is a default value (e.g., 0). Herein, the default valueis stored at offset index register 142 at power-up of the nonvolatilememory device 100. If a block address of the input address is differentfrom a block address of a previous program operation, in operation S213,the offset index m may be a value stored in offset index register 142.

In operation S221, control logic 140 sets a program start bias using theoffset index m stored at the offset index register 142. For example, theprogram start bias may be formed of a loop start voltage Vini and anoffset voltage Voffset (mISPP+β). Herein, “m” may be an offset index,“ISPP” may be a unit voltage for execution of a scan read operation, and“β” may be an offset value corresponding to a word line layer. Inexample embodiments, the offset value β may be selected from a mappingtable formed of an offset values and addresses.

In operation S222, a first program pulse according to the program startbias is applied. In operation S223, a read operation is performed usinga first verification voltage VF1. In operation S231, control logic 140determines whether the number of off cells exceeds a predetermined valuePDV, based on a result of the read operation. In example embodiments,the number of off cells may be determined using a mass bit detectionmanner.

If the number of off cells does not exceed the predetermined value PDV,in operation S232, control logic 140 increases the offset index m by 1.In operation S233, a read operation (e.g., a part of a scan readoperation) may be performed using a scan read voltage (VF1−(αISPP)×m).Herein, “a” may be a correlation coefficient between a threshold voltagelevel and a program pulse, “ISPP” may be a unit voltage, and “m” may bean offset index. Afterwards, the method proceeds to operation S231.

Returning to operation S231, if the number of off cells is determined toexceed the predetermined value PDV, in operation S240, control logic 140sets the program start bias anew. Herein, the program start bias newlyset may be formed of loop start voltage Vini, offset voltage Voffset(mISPP+β), and a loop increment ΔVpgm.

In operation S250, a program loop may be iterated according to one of adefault path and an offset path (See, FIG. 7) until a program operationis passed. A program operation may be failed when a program operation isnot passed at a last program loop.

In operation S260, if the offset index m is larger than “0”, controllogic 140 may store a value of (m−1) as a new offset index m at theoffset index register 142. Herein, operation S260 may be performed toprevent memory cells of a next word line from being over-programmed. Amanner of controlling an offset index m for prevention ofover-programming may not be limited to this disclosure. Control logic140 may determine a value of (m−2) as a new offset index m. In otherexample embodiments, the operation S260 may be skipped.

FIG. 9 is a flowchart illustrating a scan read method according to anembodiment of the inventive concept.

Referring to FIG. 9, in operation S310, control logic 140 sets a scanread region SRR according to contextual information of a nonvolatilememory device 100. The contextual information of the nonvolatile memorydevice 100 may include, for instance, wear-leveling (e.g., P/E cycle) ofa memory block, a temperature of the nonvolatile memory device 100(e.g., from an embedded temperature detector), a layer corresponding toa word line (including information corresponding to an input address), astring including a memory cell to be driven (including informationcorresponding to an input address), and so on. A top point VTP and adown point VDN (See, FIG. 6) for a scan read operation may be changedaccording to the contextual information. In operation S320, the scanread operation may be performed by a predetermined interval (e.g.,αISPP: See, FIG. 8). Herein, “α” may be a correlation coefficientbetween a threshold voltage level and a program pulse, and “ISPP” may bea unit voltage.

In the examples of FIGS. 6 to 9, a loop start voltage Vini is used as atest program pulse for offset setting. However, the inventive concept isnot limited thereto. For example, a dummy voltage Vdummy higher thanloop start voltage Vini may be used as a test program pulse at theoffset setting period to better express a characteristic of a one-shotprogram operation.

FIG. 10 is a diagram illustrating a method of programming a nonvolatilememory device according to another embodiment of the inventive concept.

Referring to FIG. 10, a dummy voltage Vdummy higher than loop startvoltage Vini is applied as a test program pulse, a read operation isperformed using a verification voltage VF3 of a third program state P3,whether to perform a scan read operation may be determined according toa result of the read operation, and a scan read operation on a scan readregion SRR may be performed from a verification voltage VF3. AlthoughFIG. 10 illustrates an example in which verification voltage VF3 ofthird program state P3 is used as a test read pulse to determine a scanread operation, the inventive concept is not limited thereto. A testread pulse used to determine a scan read operation may be determinedarbitrarily in connection with a dummy voltage Vdummy.

FIG. 11 is a timing diagram for the method of FIG. 10.

Referring to FIG. 11, a method comprises an offset setting period andprogram loops. In the offset setting period, after a dummy voltageVdummy is applied as a test program pulse, a verification read operationmay be performed using a third verification voltage VF3, and whether toperform a one-shot program operation in a default or an offset path maybe determined according to a result of the verification read operation.

A program loop period may proceed differently according to the defaultand offset paths. In contrast to the embodiment of FIG. 8, in case ofthe default path, a program loop proceeds from a program pulse accordingto a loop start voltage Vini. In the offset path, a program start bias(Vini+Voffset) determined according to a scan read operation is appliedto a program loop Loop 0, and the remaining program loops may beperformed the same as the default path. Herein, the program start biascomprises loop start voltage Vini and an offset voltage Voffset. Offsetvoltage Voffset is a voltage corresponding to a scan read region SRR(See, FIG. 10).

FIG. 12 is a flowchart illustrating the method of FIG. 10. In theexample of FIG. 12, with the exception of operations S422, S423, S433,S440, and S450, the illustrated operations are the same as correspondingoperations of FIG. 8, so a description thereof is thus omitted. Inoperation S422, a dummy voltage Vdummy is applied as a test programpulse. The dummy voltage Vdummy is higher than a loop start voltageVini. In operation S423, a verification read operation is performedusing a third verification voltage VF3. Herein, the third verificationvoltage VF3 may be a voltage for verifying a third program state P3(See, FIG. 4). In operation S433, a read operation (a part of a scanread operation) may be performed using a scan read voltage(VF3−(αISPP)×m). In operation S440, a program start bias may includeloop start voltage Vini and the offset voltage (mISPP+(3). The programstart bias in operation S440 corresponds to a value of a program startbias in S240 of FIG. 8-ΔVpgm. In operation S450, a program loop isiterated using a calculated offset voltage Voffset (See, FIGS. 10 and11) according to one of a default path and an offset path (See, FIG. 7)until a program operation is passed. A program operation may be failedwhen a program operation is not passed at a last program loop.

In the method of FIG. 12, a dummy voltage Vdummy is applied as a testprogram pulse for offset setting, a third verification voltage VF3 isapplied as a test verification pulse, an offset voltage Voffsetcorresponding to a scan read region SRR is calculated, and thecalculated offset voltage Voffset is used as a program start bias of aprogram loop.

In FIGS. 6 to 12, an offset voltage Voffset calculated in an offsetsetting period is applied to a next program loop. Also, the offsetsetting period may be prior to a program loop. However, the inventiveconcept is not limited thereto. The method may include variouscombinations of the offset setting period and program loops.

FIGS. 13A to 13E show various combinations of an offset period andprogram loops. In FIG. 13A, an offset voltage determined at an offsetsetting period is applied to next program loops. In FIG. 13B, anoperation corresponding to an offset setting period may be performedafter some program loops are executed. In FIG. 13C, an offset voltageVoffset determined at an offset setting period after some program loopsare executed is applied to next program loops. In FIG. 13D, an operationcorresponding to an offset setting period may be performed prior to eachprogram loop. In FIG. 13E, after some program loops are executed, anoperation corresponding to an offset setting period may be performedprior to the remaining program loops other than some program loops.

A one-shot method of programming a nonvolatile memory device accordingto an embodiment of the inventive concept can be applied to an on-chipbuffered programming (OBP) technique. Examples of the OBP technique aredisclosed in U.S. Patent Publication Nos. 2011/0194346, 2011/0205817,and 2011/0222342, the subject matter of which is incorporated byreference.

FIG. 14 is a block diagram illustrating an on-chip buffered programmingmethod according to an embodiment of the inventive concept.

Referring to FIG. 14, a memory system 10 comprises a nonvolatile memorydevice 300 and a memory controller 400 controlling the nonvolatilememory device 300.

With the on-chip buffered programming, data of a buffer RAM 412 inmemory controller 10 may be programmed at an SLC buffer area 322 of thenonvolatile memory device 300. Data of SLC buffer area 322 is programmedat an MLC user data area 324 of the nonvolatile memory device 120 byperforming first programming, second programming, and third programmingsequentially. Buffer RAM 412 may be, for instance, a volatile memorysuch as DRAM or SRAM. A multi-bit (e.g., 3-bit) program operation may beaccomplished by performing first programming, second programming, andthird programming sequentially. The first programming, the secondprogramming, and the third programming may perform the same multi-bitprogram operation. At least one of the first programming, the secondprogramming, and the third programming may be performed according to aone-shot program operation.

FIG. 15 is a block diagram illustrating a memory system according to anembodiment of the inventive concept.

Referring to FIG. 15, a memory system 1000 comprises at least onenonvolatile memory device 1100 and a memory controller 1200. Nonvolatilememory device 1100 may be configured to perform a one-shot programoperation described with reference to FIGS. 1 to 14.

Nonvolatile memory device 1100 may be optionally supplied with a highvoltage Vpp from an external device. Memory controller 1200 is connectedwith nonvolatile memory device 1100 via multiple channels. Memorycontroller 1200 comprises at least one Central Processing Unit (CPU)1210, a buffer memory 1220, an ECC circuit 1230, a ROM 1240, a hostinterface 1250, and a memory interface 1260. Although not shown in FIG.15, memory controller 1200 may further comprise a randomization circuitthat randomizes and de-randomizes data. Memory system 1000 may beapplicable to a perfect page new (PPN) memory. Certain examples ofmemory systems which may be adapted to incorporate certain embodimentsof the inventive concept are disclosed in U.S. Pat. No. 8,027,194 andU.S. Patent Publication No. 2010-0082890, the subject matter of whichare herein incorporated by reference.

As indicated by the foregoing, in certain embodiments of the inventiveconcept, an offset voltage may be determined according to a scanoperation, and a program start bias may be adjusted using the offsetvoltage. Nevertheless, the inventive concept is not limited thereto. Forinstance, the inventive concept may be modified such that an offset timeis determined according to a scan operation and a program start bias isadjusted using the offset time. Herein, the offset time may beassociated with a time when a pulse is applied. Moreover, as indicatedby the foregoing, performance and power consumption may be improved bycalculating an offset using a scan read operation and performing aprogram operation using the offset calculated.

The foregoing is illustrative of embodiments and is not to be construedas limiting thereof. Although a few embodiments have been described,those skilled in the art will readily appreciate that many modificationsare possible in the embodiments without departing from scope of theinventive concept as defined in the claims.

What is claimed is:
 1. A method of programming a nonvolatile memorydevice, the method comprising: applying at least one test program pulseto selected memory cells located in a scan read area of the nonvolatilememory device; performing a scan read operation on the selected memorycells, following the application of the at least one test program pulse,to determine a read operation voltage at which a predetermined number ofone-shot upper cells are identified; calculating an offset voltage basedon the difference between the determined read operation voltage and areference voltage; setting a program start bias using the offsetvoltage; and executing at least one program loop using the program startbias, wherein the scan read operation comprises, increasing/decreasingthe read operation voltage, performing another read operation, byapplying the increased/decreased read operation voltage, iteratingoperations the increasing/decreasing and the performing another readoperation until the number of off cells detected during the other readoperation exceeds a predetermined number, and establishing the readoperation voltage applied in the last iterations theincreasing/decreasing and the performing another read operation as anoffset index.